Vinyl chloride resin composition with processing aid

ABSTRACT

A composition comprising polyvinyl chloride and a novel polymer processing aid is provided. The polymer processing aid can be obtained either by blending in latex form an alkyl methacrylate copolymer (A) and a copolymer (B) comprising as its essential constituents an alkyl methacrylate, a dialkyl itaconate or an alkyl acrylate, and a diolefin, or by copolymerizing one of the copolymers in the presence of the other copolymer. 
     The polymer processing aid thus obtained improves the processability of the vinyl chloride resin composition with less reduction in impact strength.

BACKGROUND OF THE INVENTION

The present invention relates to a vinyl chloride resin composition possessing improved processability and excellent mechanical properties. More particularly, the invention relates to a vinyl chloride resin composition comprising a polymer processing aid comprising an alkyl methacrylate copolymer and a copolymer comprising as its essential constituents an alkyl methacrylate, a dialkyl itaconate or an alkyl acrylate, and a diolefin.

While vinyl chloride polymers are widely used because of their excellent physical and chemical properties, there remain various disadvantageous problems in their processability, such as a narrow range of processing temperatures at which forming or molding can be carried out due to only a small difference between the processing temperatures and thermal decomposition temperature of the polymer, and also a slow rate of gelation. It is well known that such drawbacks can be eliminated to some extent by the addition of a plasticizer. However, the addition of a plasticizer not only gives rise to other problems such as evaporation or migration of the plasticizer, but also deteriorates the mechanical properties of formed polymer products.

On the other hand, in order to obtain improved processability so that the formed products of the polymer will have a smooth surface, the rate of gelation will be increased, and deep drawing will be successfully carried out, there have been some attempts to add to a vinyl chloride polymer, as a polymer processing aid, a copolymer having compatibility therewith, such as a copolymer of styrene and acrylonitrile, a copolymer predominantly comprising methyl methacrylate and styrene, or a copolymer predominantly comprising methyl methacrylate and an alkyl acrylate.

However, all these prior art methods have serious drawbacks as follows.

A copolymer predominantly comprising styrene and acrylonitrile impairs the thermal stability of the polymer, and does not significantly improve its processability such as the gelation rate and deep drawing properties.

In comparison with the copolymer of this type, some copolymers predominantly comprising methyl methacrylate and styrene or some copolymers predominantly comprising methyl methacrylate and an alkyl acrylate effectively accelerate the gelation rate and also increase the tensile elongation at high temperatures, whereby satisfactory deep drawing properties can be obtained, and adaptability for fabrication, for example, vacuum forming, is markedly improved.

However, on the other hand, these copolymers lower the mechanical strength of a resin composition. In particular, a composition obtained by adding a polymer processing aid as described above to a composition comprising a vinyl chloride polymer and an impact strength modifier such as an acrylonitrile/butadiene/styrene copolymer or a methyl methacrylate/butadiene/styrene copolymer has a notably lowered impact strength.

SUMMARY OF THE INVENTION

As a result of our extensive research on the relationship between the processability and the mechanical properties, particularly impact strength, of a vinyl chloride polymer, it has been found that a polymer processing aid comprising a wet blend of a copolymer predominantly comprising an alkyl methacrylate and a copolymer predominantly comprising an alkyl methacrylate, a dialkyl itaconate or an alkyl acrylate, and a diolefin can impart excellent processability to the vinyl chloride polymer without impairing its mechanical properties. On the basis of this finding, we have arrived at the present invention.

The vinyl chloride resin composition of this invention possessing improved processability and excellent mechanical properties comprises

(1) 100 parts of a vinyl chloride polymer; and

(2) 0.1 to 30 parts of a polymer processing aid comprising (A) 40 to 90 parts of a copolymer comprising 80 to 100% of an alkyl methacrylate and 0 to 20% of a monomer copolymerizable therewith, and (B) 60 to 10 parts of a copolymer comprising 20 to 79% of an alkyl methacrylate, 20 to 79% of a monomer selected from dialkyl itaconates and alkyl acrylates, 1 to 49% of diolefin, and 0 to 20% of a monomer copolymerizable therewith, the copolymers (A) and (B) having been wet-blended to provide 100 parts of the polymer processing aid, all quantities expressed in parts and percentages being by weight.

DETAILED DESCRIPTION OF THE INVENTION

The polymer processing aid according to the present invention comprises a wet blend of an alkyl methacrylate copolymer (A) and a copolymer (B) comprising an alkyl methacrylate, a dialkyl itaconate or an alkyl acrylate, and a diolefin.

The term "wet blend" as used herein is intended to mean both a polymer blend obtained by blending the copolymers (A) and (B) in latex form, and a polymer blend obtained by adding and polymerizing the constituent monomers of either one of the copolymers in the presence of the other copolymer. In the latter case, the constituent monomers of the copolymer (B) may be added and polymerized in the presence of the copolymer (A) or vice versa.

Of these blending methods including the latex blending, a particularly preferred method comprises adding the constituent monomers of the copolymer (B) to the copolymer (A) and subjecting the same to polymerization. This method, as compared with the other methods, effectively prevents occurrence of ungelled particles (fish eyes), and further ensures improved surface smoothness and transparency. A polymer blend obtained by a method other than the above described wet-blending, for example, a polymer blend obtained by blending the copolymers (A) and (B) in powder form, will result in lower processability and transparency of the composition obtained.

The term "addition and polymerization", or "polymerization of monomers in the presence of a copolymer" is herein used in a broader sense than "graft polymerization", and all of the monomers to be charged in the second-stage polymerization, which is carried out after the first-stage polymerization, need not necessarily be grafted on the copolymer obtained in the first stage, but part of the monomers may be polymerized in an ungrafted state to give a polymer blend.

Relative to 40 to 90 parts of the copolymer (A), 60 to 10 parts of the copolymer (B) is used in accordance with the present invention. A smaller quantity of the copolymer (A) cannot produce a satisfactory effect of improving the processability of a resin composition, while the use of this copolymer in greater quantity is undesirable because many ungelled particles occur.

The copolymer (A) comprises 80 to 100%, preferably 90 to 100%, of an alkyl methacrylate; and 0 to 20%, preferably 0 to 10%, of one or more monomers copolymerizable therewith.

For the alkyl methacrylate, those having 1 to 8, preferably 1 to 4, carbon atoms in the alkyl group are used, and methyl methacrylate is particularly preferred.

The addition of a smaller quantity of the alkyl methacrylate to the copolymer (A) is undesirable because the effect of improving the processability of the resin composition becomes poor.

Examples of monomers copolymerizable with the alkyl methacrylate are alkyl acrylates such as methyl acrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate; aromatic vinyl compounds such as styrene, α-methyl styrene, and chlorostyrene; unsaturated nitriles such as acrylonitrile, and methacrylonitrile; vinyl ethers such as methyl vinyl ether, and ethyl vinyl ether; vinyl ketones such as methyl vinyl ketone, and ethyl vinyl ketone; and vinyl esters such as vinyl acetate.

The copolymer (B) comprises 20 to 79%, preferably 30 to 69%, of an alkyl methacrylate; 20 to 79%, preferably 30 to 69%, of a dialkyl itaconate or an alkyl acrylate; 1 to 49%, preferably 1 to 30%, of a diolefin; and 0 to 20% of one or more monomers copolymerizable therewith.

If the quantity of the alkyl methacrylate is smaller and that of the dialkyl itaconate or alkyl acrylate is greater than the quantities specified above, the effect of improving the processability of a resin composition will be poor. Conversely, in case the alkyl methacrylate is used in greater quantities and the dialkyl itaconate or alkyl acrylate is used in smaller quantities, the polymer processing aid will not be uniformly dispersed in a vinyl chloride polymer under ordinary processing conditions, and there will remain numerous ungelled particles.

When the dialkyl itaconate and alkyl acrylate are used in combination, the quantity specified above refers to the total quantity of each combination of the compounds.

The diolefin is added in a quantity of 1 to 49%, preferably 1 to 30%, of the copolymer (B). Less than 1% of the diolefin deteriorates the mechanical properties, particularly the impact strength, of the resin composition, while the use of diolefin in excess of the above quantity converts the copolymer (A) into a rubber, resulting in poor thermal stability of the composition.

For the alkyl methacrylate which is also one of the constituents of the copolymer (B), an alkyl methacrylate having 1 to 8, preferably 1 to 4, carbon atoms in the alkyl group is used similarly as in the case of the alkyl methacrylate constituting the copolymer (A), and methyl methacrylate is most beneficial.

Suitable examples of the dialkyl itaconates to be used in the copolymer (B) are those having 1 to 18, preferably 1 to 10, carbon atoms in the alkyl group, and diethyl itaconate and dibutyl itaconate are particularly suitable.

For the alkyl acrylate, methyl acrylate, ethyl acrylate, n-butyl acrylate, or 2-ethylhexyl acrylate is used, and ethyl acrylate and n-butyl acrylate are most preferred.

For the diolefin, butadiene, isoprene, or chloroprene is used.

Examples of monomers copolymerizable with the alkyl methacrylate, dialkyl itaconate or alkyl acrylate, and diolefin are aromatic vinyl monomers such as styrene, α-methylstyrene, chlorostyrene, and vinylnaphthalene; unsaturated nitriles such as acrylonitrile, and methacrylonitrile; vinyl ethers such as methyl vinyl ether, and ethyl vinyl ether; vinyl ketones such as methyl vinyl ketone, and ethyl vinyl ketone; vinyl esters such as vinyl acetate; and polyfunctional monomers such as divinylbenzene, and ethylene glycol dimethacrylate. One or more of these monomers can be used in a quantity ranging from 0 to 20%.

All ratios herein specified refer to the ratios between the contents of the respective components of the composition, polymer processing aid or copolymer. However, since the degree of polymerization required to obtain each polymer, including those produced in the Examples set forth hereinlater, is ordinarily 95% or higher, the above ratios can be regarded as substantially identical with the ratios between the monomers charged.

In order to obtain the polymer processing aid of the present invention, each of the copolymers (A) and (B) is preferably prepared by emulsion polymerization wherein a known emulsifier, and a water-soluble, oil-soluble or redox polymerization initiator can be utilized.

The degree of polymerization can be freely controlled by conventional combinations of polymerization temperatures and chain transfer agents. It is preferable that the degree of polymerization of the polymer processing aid be such that the reduced viscosity thereof is at least 0.1 dl/g, preferably at least 0.5 dl/g, as measured at 20° C. with a solution of 0.4 g of the polymer processing aid in 100 cc of chloroform.

The vinyl chloride polymers to be blended with the polymer processing aid according to the present invention include: polyvinyl chloride; a copolymer of at least 80% of vinyl chloride and one or more monomers copolymerizable therewith, such as vinylidene chloride, vinyl acetate, acrylic ester, acrylonitrile, ethylene, and propylene; derivatives of the polyvinyl chloride and the copolymer, such as resins obtained by further chlorination of the above mentioned polymers; or a mixture of two or more polymers selected from the above groups.

The polymer processing aid of this invention is added in a quantity of 0.1 to 30 parts, preferably 0.5 to 10 parts, per 100 parts of a vinyl chloride polymer. If this aid is added in smaller quantities, the effect of improving the processability of the polymer becomes poor, while the use of this aid in greater quantities deteriorates the innate properties of the vinyl chloride polymer.

The polymer processing aid according to the present invention is particularly effective when used in combination with a conventional impact strength modifier for vinyl chloride polymers such as an acrylonitrile/butadiene/styrene copolymer and a methyl methacrylate/butadiene/styrene copolymer, and can improve the processability of the resin composition obtained without appreciably lowering the impact strength thereof as compared with known polymer processing aids.

The impact strength modifier is preferably used in a quantity of 1 to 30 parts per 100 parts of a vinyl chloride polymer.

If desired, the resin composition of the present invention may comprise, in addition to the aforesaid vinyl chloride polymer and polymer processing aid, optional additives such as stabilizers, antioxidants, ultraviolet ray absorbents, lubricants, impact strength modifiers, plasticizers, coloring agents, fillers, and blowing agents in conventional quantities.

In order to indicate more fully the nature and utility of this invention, the following specific examples of practice constituting preferred embodiments of the invention and comparison examples are set forth, it being understood that these examples are presented as illustrative only and are not intended to limit the scope of the invention.

EXAMPLE 1

300 parts of distilled water, 1.0 part of sodium dodecylbenzenesulfonate which had been dissolved in water, 0.03 part of potassium persulfate, 0.0075 part of sodium hydrogensulfite, 75 parts of methyl methacrylate, and 0.045 part of n-dodecyl mercaptan were charged into a reactor provided with a stirrer. The atmosphere within the reactor was purged with nitrogen, and then the temperature in the reactor was raised to 50° C. with stirring. The mixture obtained was subjected to reaction at this temperature for 6 hours. Thereafter, 0.01 part of potassium persulfate, 0.0025 part of sodium hydrogensulfite, 11 parts of methyl methacrylate, 10 parts of dibutyl itaconate, 4 parts of butadiene, and 0.25 part of n-dodecyl mercaptan were added, and the resulting mixture was subjected to reaction at 50° C. for 15 hours. After cooling of the reaction mixture, the latex obtained was subjected to precipitation with aluminium sulfate, and subsequently neutralized, filtered, washed with water, and dried, whereupon a polymer (Polymer Processing Aid No. 1) was obtained. The conversion was nearly 100%.

EXAMPLE 2

300 parts of distilled water, 1.0 part of sodium dodecylbenzenesulfonate which had been dissolved in water, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 50 parts of methyl methacrylate, and 0.03 part of n-dodecyl mercaptan were charged into a reactor provided with a stirrer. The atmosphere within the reactor was purged with nitrogen, and then the temperature in the reactor was raised to 50° C. with stirring. The mixture obtained was subjected to reaction at this temperature for 6 hours. Thereafter, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 20 parts of methyl methacrylate, 20 parts of dibutyl itaconate, 10 parts of butadiene, and 0.5 part of n-dodecyl mercaptan were added, and the resulting mixture was subjected to reaction at 50° C. for 15 hours. After cooling of the reaction mixture, the latex obtained was subjected to precipitation with aluminium sulfate, and subsequently neutralized, filtered, washed with water, and dried, whereupon a polymer (Polymer Processing Aid No. 2) was obtained. The conversion was nearly 100%.

EXAMPLE 3

300 parts of distilled water, 1.0 part of sodium dodecylbenzenesulfonate, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 20 parts of methyl methacrylate, 20 parts of dibutyl itaconate, 10 parts of butadiene, and 0.5 part of n-dodecyl mercaptan were charged into a reactor provided with a stirrer. The atmosphere within the reactor was purged with nitrogen, and then the temperature in the reactor was raised to 50° C. with stirring. The mixture obtained was subjected to reaction at this temperature for 15 hours. Thereafter, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 50 parts of methyl methacrylate, and 0.03 part of n-dodecyl mercaptan were added, and the resulting mixture was subjected to reaction at 50° C. for 15 hours. After cooling of the reaction mixture, the latex obtained was subjected to precipitation with aluminium sulfate, and subsequently neutralized, filtered, washed with water, and dried, whereupon a polymer (Polymer Processing Aid No. 3) was obtained. The conversion was nearly 100%.

EXAMPLE 4

300 parts of distilled water, 1.0 part of sodium dodecylbenzenesulfonate, 0.04 part of potassium persulfate, 0.01 part of sodium hydrogensulfite, 100 parts of methyl methacrylate, and 0.06 part of n-dodecyl mercaptan were charged into a reactor provided with a stirrer. The atmosphere within the reactor was purged with nitrogen, and then the temperature in the reactor was raised to 50° C. with stirring. The mixture obtained was subjected to reaction at this temperature for 15 hours to obtain a polymer latex (A).

Separately, a composition comprising 300 parts of water, 1.0 part of sodium dodecylbenzenesulfonate, 0.04 part of potassium persulfate, 0.01 part of sodium hydrogensulfite, 42 parts of styrene, 42 parts of butyl acrylate, 16 parts of butadiene, and 1.0 part of n-dodecyl mercaptan was subjected to polymerization at 50° C. for 15 hours to obtain a polymer latex (B).

The polymer latexes (A) and (B), after being thoroughly mixed with each other, were subjected to a post-treatment under the same conditions as in Example 1 to obtain a polymer (Polymer Processing Aid No. 4).

COMPARISON EXAMPLE 1

300 parts of distilled water, 1.0 part of sodium dodecylbenzenesulfonate which had been dissolved in water, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 50 parts of methyl methacrylate, and 0.03 part of n-dodecyl mercaptan were charged into a reactor provided with a stirrer. The atmosphere within the reactor was purged with nitrogen, and then the temperature in the reactor was raised to 50° C. with stirring. The mixture obtained was subjected to reaction at this temperature for 6 hours. Thereafter, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 25 parts of methyl methacrylate, 25 parts of dibutyl itaconate, and 0.5 part of n-dodecyl mercaptan were added, and the resulting mixture was subjected to reaction at 50° C. for 15 hours. After cooling of the reaction mixture, the latex obtained was subjected to precipitation with aluminium sulfate, and subsequently neutralized, filtered, washed with water, and dried, whereupon a polymer (Polymer Processing Aid No. 5) was obtained.

EXAMPLE 5

300 parts of distilled water, 1.0 part of sodium dodecylbenzenesulfonate which had been dissolved in water, 0.03 part of potassium persulfate, 0.0075 part of sodium hydrogensulfite, 75 parts of methyl methacrylate, and 0.045 part of n-dodecyl mercaptan were charged into a reactor provided with a stirrer. The atmosphere within the reactor was purged with nitrogen, and then the temperature in the reactor was raised to 50° C. with stirring. The mixture obtained was subjected to reaction at this temperature for 6 hours. Thereafter, 0.01 part of potassium persulfate, 0.0025 part of sodium hydrogensulfite, 11 parts of methyl methacrylate, 10 parts of butyl acrylate, 4 parts of butadiene, and 0.25 part of n-dodecyl mercaptan were added, and the resulting mixture was subjected to reaction at 50° C. for 15 hours. After cooling of the reaction mixture, the latex obtained was subjected to precipitation with aluminium sulfate, and subsequently neutralized, filtered, washed with water, and dried, whereupon a polymer (Polymer Processing Aid No. 6) was obtained. The conversion was nearly 100%.

EXAMPLE 6

300 parts of distilled water, 1.0 part of sodium dodecylbenzenesulfonate which had been dissolved in water, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 50 parts of methyl methacrylate, and 0.03 part of n-dodecyl mercaptan were charged into a reactor provided with a stirrer. The atmosphere within the reactor was purged with nitrogen, and then the temperature in the reactor was raised to 50° C. with stirring. The mixture obtained was subjected to reaction at this temperature for 6 hours. Thereafter, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 20 parts of methyl methacrylate, 20 parts of butyl acrylate, 10 parts of butadiene, and 0.6 part of n-dodecyl mercaptan were added, and the resulting mixture was subjected to reaction at 50° C. for 15 hours. After cooling of the reaction mixture, the latex obtained was subjected to precipitation with aluminium sulfate, and subsequently neutralized, filtered, washed with water, and dried, whereupon a polymer (Polymer Processing Aid No. 7) was obtained. The conversion was nearly 100%.

EXAMPLE 7

300 parts of distilled water, 1.0 part of sodium dodecylbenzenesulfonate, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 20 parts of methyl methacrylate, 20 parts of butyl acrylate, 10 parts of butadiene, and 0.6 part of n-dodecyl mercaptan were charged into a reactor provided with a stirrer. The atmosphere within the reactor was purged with nitrogen, and then the temperature in the reactor was raised to 50° C. with stirring. The mixture obtained was subjected to reaction at this temperature for 15 hours. Thereafter, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 50 parts of methyl methacrylate, and 0.03 part of n-dodecyl mercaptan were added, and the resulting mixture was subjected to reaction at 50° C. for 15 hours. After cooling of the reaction mixture, the latex obtained was subjected to precipitation with aluminium sulfate, and subsequently neutralized, filtered, washed with water, and dried, whereupon a polymer (Polymer Processing Aid No. 8) was obtained. The conversion was nearly 100%.

EXAMPLE 8

300 parts of distilled water, 1.0 part of sodium dodecylbenzenesulfonate, 0.04 part of potassium persulfate, 0.01 part of sodium hydrogensulfite, 100 parts of methyl methacrylate, and 0.06 part of n-dodecyl mercaptan were charged into a reactor provided with a stirrer. The atmosphere within the reactor was purged with nitrogen, and then the temperature in the reactor was raised to 50° C. with stirring. The mixture obtained was subjected to reaction at this temperature for 15 hours to obtain a polymer latex (A').

Separately, a composition comprising 300 parts of water, 1.0 part of sodium dodecylbenzenesulfonate, 0.04 part of potassium persulfate, 0.01 part of sodium hydrogensulfite, 40 parts of styrene, 40 parts of butyl acrylate, 20 parts of butadiene, and 1.2 parts of n-dodecyl mercaptan was subjected to polymerization at 50° C. for 15 hours to obtain a polymer latex (B').

The polymer latexes (A') and (B'), after being thoroughly mixed with each other, were subjected to a post-treatment under the same conditions as in Example 1 to obtain a polymer (Polymer Processing Aid No. 9).

COMPARISON EXAMPLE 2

300 parts of distilled water, 1.0 part of sodium dodecylbenzenesulfonate which had been dissolved in water, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 50 parts of methyl methacrylate, and 0.03 part of n-dodecyl mercaptan were charged into a reactor provided with a stirrer. The atmosphere within the reactor was purged with nitrogen, and the temperature in the reactor was then raised to 50° C. with stirring. The mixture obtained was subjected to reaction at this temperature for 6 hours.

Thereafter, 0.02 part of potassium persulfate, 0.005 part of sodium hydrogensulfite, 25 parts of methyl methacrylate, 25 parts of butyl acrylate, and 0.5 part of n-dodecyl mercaptan were added, and the resulting mixture was subjected to reaction at 50° C. for 15 hours. After cooling, the latex obtained was subjected to precipitation with aluminium sulfate, and subsequently neutralized, filtered, washed with water, and dried, whereupon a polymer (Polymer Processing Aid No. 10) was obtained.

Physical Property Test

5 and 10 parts, respectively, of the polymer processing aids obtained as described above and a commercially available polymer processing aid predominantly comprising methyl methacrylate and an alkyl acrylate each were blended with 90 parts of polyvinyl chloride (average degree of polymerization: 700), 10 parts of an impact strength modifier (methyl methacrylate/butadiene/styrene copolymer mfd. by Kureha Kagaku Kogyo, K. K., Japan: BTA-III), 2 parts of a dioctyltinmercapto compound, 0.8 part of stearyl alcohol, and 0.2 part of partially saponified butylene glycol montanate. Each of the resulting resin compositions was tested for the properties shown in Table 1, and the results set forth in Table 2 were obtained.

Similarly, a composition prepared in the same manner as is described above except that no polymer processing aid was used was tested. The results obtained are summarized in Table 2.

                  TABLE 1                                                          ______________________________________                                         Strength & Elongation:                                                         Each polymer composition was kneaded for 3 min.                                with rolls having a surface temperature of 160° C.,                     and pressed for 3 min. at 200° C. to prepare a poly-                    mer sheet sample of 1.0 mm thickness. This sheet                               sample was cut into strips from which specimens                                formed into JIS-No. 1 dumbbell shape were pre-                                 pared through a plain cutter. The strength and                                 elongation of each dumbbell specimen was measured                              by means of Tensilon UTM-L (mfd. by Toyo Sokki                                 K.K., Japan).                                                                         [Measurement Conditions]                                                       Temperature:                                                                              150° C.                                                      Sample length:                                                                            40 mm                                                               Pulling rate:                                                                             500 mm/min.                                                  Transparency:                                                                  Each polymer composition was kneaded for 3 min.                                with rolls having a surface temperature of 160° C.,                     and pressed for 3 min. at 200° C. to prepare a poly-                    mer sheet sample of 3 mm thickness. The parallel                               ray transmittance (Tp) and haze (H) of this sheet                              sample were measured by means of a hazeometer of                               integrating sphere type with C-filter in accord-                               ance with JIS K-6714.                                                          Impact Strength (Izod Impact Strength):                                        Each polymer composition was kneaded for 3 min.                                with rolls having a surface temperature of 160° C.,                     and pressed for 7 min. at 200° C. to prepare a                          polymer sheet sample of 6 mm thickness. This                                   sheet sample was formed into specimens with V-                                 notches in accordance with ASTM D-256-54T. The                                 Izod impact strength of each specimen was measur-                              ed at 23° C.                                                            ______________________________________                                    

                  TABLE 2                                                          ______________________________________                                         Poly-  Q'ty of  Properties of Resin Composition                                mer    Polymer  Strength & Elon-      Izod                                     Proce- Proces-  gation        Trans-  Impact                                   ssing  sing Aid Elonga-  Breaking                                                                              parency Strength                               Aid    Added    tion     Strength                                                                              Tp   H    (Kg ·                       No.    (part)   (%)      (Kg/cm.sup.2)                                                                         (%)  (%)  cm/cm)                               ______________________________________                                         Example                                                                        (1)    5        190      7.7    82.8 4.1  71.1                                        10       291      8.5    79.0 5.7  18.7                                 (2)    5        183      7.6    82.9 4.0  80.3                                        10       281      8.1    78.3 6.2  57.4                                 (3)    5        181      7.6    82.4 4.1  81.2                                        10       275      8.1    77.2 6.2  58.5                                 (4)    5        176      7.5    81.5 4.2  79.5                                        10       282      8.3    75.4 8.7  59.6                                 (6)    5        189      7.7    82.7 4.1  74.2                                        10       296      8.6    76.4 7.9  18.9                                 (7)    5        180      7.5    82.9 3.9  81.9                                        10       277      8.0    76.4 7.7  59.7                                 (8)    5        181      7.6    82.7 4.0  79.8                                        10       280      8.2    75.0 8.9  58.0                                 (9)    5        178      7.6    81.9 4.2  82.3                                        10       283      8.2    74.3 9.0  60.7                                 Com-                                                                           parison                                                                        Example                                                                        (5)    5        188      7.6    82.9 4.0  73.2                                        10       290      8.0    79.3 6.1  8.2                                  (10)   5        190      7.6    82.0 4.1  68.1                                        10       290      8.3    78.0 6.3  7.3                                  Commer-                                                                        cially                                                                         avail-                                                                         able   5        186      7.6    81.6 5.1  75.2                                 polymer                                                                               10       281      8.5    79.5 6.0  7.8                                  process-                                                                       ing aid                                                                        None   --       145      7.8    83.0 3.8  106                                  ______________________________________                                    

As is apparent from Table 2, a resin composition comprising the polymer processing aid of the present invention possesses higher impact strength than a resin composition comprising a polymer processing aid containing no diolefin, and still has substantially the same degree of strength, elongation and transparency. 

What is claimed is:
 1. A vinyl chloride resin composition comprising:(1) 100 parts of a vinyl chloride polymer; and (2) 0.1 to 30 parts of a polymer processing aid comprising:(A) 40 to 90 parts of a copolymer comprising 80 to 100% of an alkyl methacrylate, and 0 to 20% of a monomer copolymerizable therewith; and (B) 60 to 10 parts of a copolymer comprising 20 to 79% of an alkyl methacrylate, 20 to 79% of a monomer selected from the group consisting of a dialkyl itaconate and an alkyl acrylate, 1 to 49% of a diolefin, and 0 to 20% of a monomer copolymerizable therewith, 100 parts of said polymer processing aid having been obtained by polymerizing 60 to 10 parts of the constituent monomers of the copolymer (B) in the presence of 40 to 90 parts of the copolymer (A), all quantities expressed in parts and percentages being by weight.
 2. A vinyl chloride resin composition as claimed in claim 1, wherein the copolymer (B) comprises 30 to 69% of an alkyl methacrylate, 30 to 69% of a dialkyl itaconate or alkyl acrylate, and 1 to 30% of a diolefin.
 3. A vinyl chloride resin composition as claimed in claim 1, wherein the alkyl methacrylate has an alkyl group of 1 to 8 carbon atoms.
 4. A vinyl chloride resin composition as claimed in claim 1, wherein the dialkyl itaconate has 1 to 18 carbon atoms in each alkyl group.
 5. A vinyl chloride resin composition as claimed in claim 1, wherein the alkyl acrylate is selected from the group consisting of methyl acrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate.
 6. A vinyl chloride resin composition as claimed in claim 1, wherein the diolefin is selected from the group consisting of butadiene, isoprene, and chloroprene.
 7. A vinyl chloride resin composition as claimed in claim 1, wherein the composition further comprises 1 to 30 parts by weight of an impact strength modifier selected from the group consisting of acrylonitrile/butadiene/styrene copolymers and methyl methacrylate/butadiene/styrene copolymers per 100 parts by weight of the vinyl chloride polymer. 